Skylights have traditionally been formed as structures similar to windows, comprising a frame with sheet glazing to admit light through an aperture in a roof surface.
More recently a form of skylight, shown schematically in FIG. 1, which has gained wide acceptance, includes a transparent dome installed above an aperture in the roof surface. A cylindrical, so-called light tube, extends from below the lower periphery of the dome, through the roof aperture and down to the ceiling. The interior surface of this cylindrical light tube is highly reflective so as to reflect angled light entering the dome down to a diffuser at the lower end of the tube, generally at ceiling level.
Although these dome and light tube skylights are effective, the dome, being of a simple, generally constant wall thickness, has little effect on the direction of incident light passing through the dome and entering the light tube.
An improvement in the light gathering ability of a skylight dome was disclosed in U.S. Pat. No. 7,546,709 in which the interior surface of the dome is provided with an arrangement of refracting elements, somewhat in the manner of a Fresnel lens. The refracting elements are arranged as continuous circles of ridges parallel to the lower periphery of the dome. Although an advance over plain light admitting domes, the particular arrangement of the refractive surfaces is only optimally effective in directing incident rays of sunlight impinging on the dome in regions close to planes passing through the dome's axis and aligned with the direction of the sun. Sunlight striking the dome away from this optimal region is increasingly either largely reflected off the dome surface or not optimally refracted into the light tube.
It is an object of the present invention to address or at least ameliorate some of the above disadvantages.